Submitted as: model description paper
06 Apr 2022
Submitted as: model description paper | 06 Apr 2022
Status: this preprint is currently under review for the journal GMD.

FESDIA (v1.0): Exploring temporal variations of sediment biogeochemistry under the influence of flood events using numerical modelling

Stanley Ifeanyi Nmor1, Eric Viollier1, Lucie Pastor2, Bruno Lansard1, Christophe Rabouille1, and Karline Soetaert3 Stanley Ifeanyi Nmor et al.
  • 1Laboratoire des Sciences du Climat et de l’Environnement, LSCE/IPSL,CEA-CNRS-UVSQ-Université Paris Saclay, 91198 Gif sur Yvette, France
  • 2Laboratoire Environnement Profond, Ifremer – Centre de Bretagne, 29280 Plouzané, France
  • 3Royal Netherlands Institute of Sea Research (NIOZ), Department of Estuarine and Delta Systems, Korringaweg 7, P.O. Box 140, 4401 NT Yerseke, The Netherlands

Abstract. Episodic events of flood deposit in coastal environments are characterized by deposition of large quantities of sediment containing reactive organic matter within short periods of time. While steady-state modelling is common in sediment biogeochemical modelling, the inclusion of these events in current early diagenesis models has yet to be demonstrated. We adapted an existing model of early diagenetic processes to include the ability to mimic an immediate organic carbon deposition. The new model version was able to reproduce the basic trends from field sediment porewater data affected by the November 2008 flood event in the Rhone River prodelta. Simulation experiments on two end-member scenarios of sediment characteristics dictated by field observation, (1-high thickness deposit, with low TOC and 2-low thickness, with high TOC), reveal contrasting evolutions of post-depositional profiles. A first-order approximation of the differences between subsequent profiles was used to characterize the timing of recovery (i.e relaxation time) from this alteration. Our results indicate a longer relaxation time of approximately 4 months for SO42- and 5 months for DIC in the first scenario and less than 3 months for the second scenario which agreed with timescale observed in the field. A sensitivity analysis across a spectrum of these end-member cases for the organic carbon content (described as the enrichment factor α) and for sediment thickness – indicates that the relaxation time for oxygen, sulfate, and DIC decreases with increasing organic enrichment for a sediment deposition that is less 5 cm. However, for larger deposits (> 14 cm), the relaxation time for oxygen, sulfate and DIC increases with α. This can be related to the depth dependent availability of oxidant and the diffusion of species. This study emphasizes the significance of these sediment characteristics in determining the sediment’s short-term response in the presence of an episodic event. Furthermore, the model described here provides a useful tool to better understand the magnitude and dynamics of flooding event on biogeochemical reactions on the seafloor.

Stanley Ifeanyi Nmor et al.

Status: open (until 09 Jun 2022)

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  • RC1: 'Comment on gmd-2022-84', Anonymous Referee #1, 19 May 2022 reply

Stanley Ifeanyi Nmor et al.

Stanley Ifeanyi Nmor et al.


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Short summary
The coastal marine environment serves as a transition zone in the land-ocean continuum and is susceptible to episodic phenomena such as flash floods, which cause massive organic matter deposition. Here, we present a model of sediment early diagenesis that explicitly describes this type of deposition while also incorporating unique flood deposit characteristics. This model can be used to investigate the temporal evolution of marine sediments following abrupt changes in environmental conditions.